It is common practice in the food industry to pack liquid contents such as juice or milk in packaging containers of single-use disposable type which are manufactured from a flexible, liquid-tight packaging material. The substantially parallelepipedic packaging containers which are marketed under the brand name Tetra Brik.RTM. are described in greater detail in European Patent No. EP 91712, to which reference is now made, and are thus manufactured from a flexible packaging laminate which comprises a carrier or core layer of fibre material, for example paper, which is coated on each side with relatively thin layers of thermoplastic material, normally polyethylene. The packaging laminate may also include further material layers, such as barrier layers of metal or other barrier materials in order to provide improved protection against light or oxygen gas when particularly sensitive products are to be packed.
In the manufacture of the above-outlined prior art packaging containers, a packing or filling machine is employed which stepwise reforms a preferably web-shaped packaging laminate into individual, filled packaging containers. In order to facilitate the reforming process, the packaging laminate is provided with a pattern of fold or crease lines which are formed by pressing of the packaging laminate between rollers with cooperating ridges and depressions which, above all because of softening of the fibre layer, impart to the material a tendency to be folded along the weakened, linear areas created in this process. The reforming of the original, substantially cushion-shaped filled and sealed packaging containers into parallelepipedic form will hereby be facilitated. The so-called final forming above all comprises flat-pressing, inward folding and sealing of formed corner flaps to the outside of the packaging container, so that a substantially parallelepipedic configuration is achieved. Since, principally for economic reasons, attempts are made in the art to minimise the quantity of material included in the packaging laminate, the packaging laminate itself is relatively thin, with the result that the difference in folding tendency between the parts of the laminate provided with fold or crease lines and the unaffected parts is relatively slight. Consequently, the reforming of the packaging laminate into packaging containers and, in particular the so-called final forming operation may result in a packaging container which not always obtains the desired, well-defined edges and corners but tends to display a more rounded transitional area between the different wall surfaces of the packaging container disposed at angles to one another. A more undefined configuration further entails the disadvantage that the packaging container will, in the finished state, be perceived by the consumer as more markedly yielding and unstable, which may impede the consumer's handling of the packaging container, primarily in connection with pouring of the contents from the container.
The method and the apparatus according to the present invention may naturally also be employed in other, for instance prismatic configurations of packaging containers which are manufactured by folding and sealing of flexible packaging material.
There is thus a general need in the art to realise a packaging container of the above-outlined type possessing well-defined--or calibrated--configuration and improved steadiness and stability. With a view to realising this object, attempts have been made in the art to modify the packaging laminate by incorporating layers of different material types and properties, but this has however most generally entailed that the packaging laminate becomes more expensive. Trials have also been carried out with different types of crease or weakening lines, with the intention of realising a more manifest weakening of the material so that folding and forming are facilitated, but no tangible improvement has been achieved. In order to obtain a packaging container possessing well-defined or calibrated configuration and improved stability, one option which has been indicated in the art is to increase the thickness of the packaging laminate and, in particular, the fibre layer, which naturally entails increased costs and, as a result, has been put into practice to only a limited extent.